The Working Cell:Energy from Food

Chapter 7Sections 1-4

Sunlight Powers Life

Food Stores Chemical Energy

Energy is the ability to do work (or applying a force across a distance)

Two Basic Types of Energy:

Kinetic Energy - the energy of motion

Potential Energy - stored energy due to position or arrangement

Energy Transfers

When you slide down a slide into a swimming pool, you convert potential energy into kinetic energy.

As your body collides with air and water molecules, you transfer energy to the molecules in random directions. That random molecular motion is thermal energy or HEAT.

The Energy to Move Again

The thermal energy created CANNOT be retrieved and put back to work inside the body.

So to move again, you must use a fresh supply of energy.

That energy is the chemical energy stored in FOOD (organic molecules).

Making Chemical Energy Available for Work

Cells break complex organic molecules into smaller molecules with less chemical energy

This process is called cellular respiration

Glucose + Oxygen → Carbon Dioxide + Water + Energy

40%

Chemical

60%

Thermal

Measuring Energy

Energy is measured in units called calories

A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1◦C

1000 calories = 1 kcal or Calorie (a nutritional calorie)

However, food is not used directly by cells to do work, it must be converted into another usable form called ATP.

What is ATP?

ATP is called the "currency" of the cell– ATP is a small packet of Energy that can be

used a little at a time, like coins– ATP is constantly reused and recycled– You can’t buy things without $$, cells can’t

Work without Energy from ATP

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ATP Structure

ATP consists of:

– adenine

– ribose (a 5-carbon sugar)

– 3 phosphate groups (TP = tri phosphate)

Adenine

ATP

Ribose 3 Phosphate groups

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Chemical Energy and ATP– Storing Energy

• ADP has two phosphate groups instead of three.• A cell can store small amounts of energy by adding a

phosphate group to ADP.

ADPATP

Energy

Energy

Partiallycharged battery

Fullycharged battery

+

Adenosine Diphosphate (ADP) + Phosphate

Adenosine Triphosphate (ATP)

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Chemical Energy and ATP

P

ADP

2 Phosphate groups

– Releasing EnergyEnergy stored in ATP is released by breaking the chemical bond between the second and third phosphates.

The ATP Cycle

ATP → ADP + phosphate + energy for Work

ADP + Energy (from food) + phosphate → ATP

Why does the process of cellular respiration release energy?

• In an atom the positive nucleus attracts negative electrons

• When electron “fall” towards the nucleus, potential energy is released

• OXYGEN attracts electrons very strongly compared to carbon and hydrogen

• During respiration, the carbon-hydrogen bonds in sugar are rearranged to bond with oxygen instead (CO2 + H2O)

Electron Transport Chains

• Instead of releasing all the energy stored in food at once (like burning), cellular respiration releases the energy in controlled “steps”

• Glucose gets broken down in several steps, transferring electrons to molecules called electron carriers

• The electron carriers accept high-energy electrons from glucose and pass them along a chain of electron carriers (ETC) releasing ATP

• Oxygen comes in at the end to accept 2 low energy electrons, bond with hydrogen, and form water

ETC Animation